Process of treating cellulose derivative sheets



Aprill 7, 1936..

J. B. WELLS if:

PROCESS OF TREATING CELLULOSE DERIVATIVE SHEETS Filed May 26, 1933AIROUTLET.

HOT AIR INLET.

elected Apr '7, W3

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This invention. relates to processes oi lecturing cellulose esterproducts and more er ticularly to processes for treating cellulose estersheet material with various solutions or susnensions to import improvedproperties thereto. Specifically, thev invention relates to thetreutment of sheeting particularly thin sheeting, hrolo only while it isin u relatively plastic condition end contains a. considerulolcproportion oi" solvent and in all events heiore it lies heen removedirons the surface upon which it wus originally cost. in the manufactureof cellulose derivative sheeting e. suitable solution. oi e celluloseester is spread or flowed upon scestins surtuce, end the solventsremoved therefrom by evu ooreticu. Que oi the most commonly employedmethods is to maize up 2. cellulose ester solution or done of the propercomposition and viscosity by dissolving the cellulose ester inappropriate solvents end ieedine; this done irom e. hopper, regulated togive the desired thickness, upon the suriuce ot a slowly rotatingcasting wheel. The solution hows out upon the curious oi the wheel endno the latter rotates a current oi sir or other sultehlc evaporativemedium is hroueht in coutoct with the sheet thus termed, cousins; thesolvent to he evaporated therefrom. Before the wheel has rotated throughor complete revolution most oi the solvents hove evaporated and thesheet is then in o. condition in which it may he stripped from thesuriace oi? the wheel uud subjected to curing treatment to iurtherreduce its residual solvent content and bring its choreoteristics withinthe desired rouge.

it is often desired to treat-sheeting produced in this manner to impartto it certein properties such as to impart color or to treat themuteriul with various solutions for the purpose oi coating orlubricating it and for muny other purposes. It has heretofore been thepractice to carry out such treatment, either alter the sheet hus'heencompletely cured, or at some stage of the curing operation, that is;alter the sheet has been removed from the casting surface. Suchtreatment has been attended with varying degrees oi success, dependingsomewhat upon the nature and thickness oi the sheet end the nature oithe solution or liquid applied .thereto. However, the results obtained,for example, in applyins solutions or suspensions of colored material tocellulose derivative sheeting have not been wholly satisfactory due-tolack of proper penetration of the coloring or other'solutlon into thecured sheet and to the very marked tendency of the material to wrinkle.50 marked has been (or in this wrne tendency, particularly with the tertypes oi cellulose derivative sheeting de signed for wrapping purposes,that it has loeeri oructicslly out oi the question to eerily coloring orother types of treeting solutions to this type oi material. 7

it is the principal object oi the present invention to overcome theshove mentioned difilcuities end to provide processes in which cellulosederiv utive sheeting may he treated with various impresenting solutionsor suspensions end in which no wrinkling or other adverse distortion ofthe materiel takes place. 0 A specific ololect of the in vention is toprovide u process for coloring thin cellulose derivative sheetingbyapplication ct e solution or suspension of coloring mutter. ohiects willhereinuiter appear.

The invention is more iully set forth in the lot lowing descriptiontulteu in connection with the 'uccou'ioanying drawing! in which hitsnumerals are spelled to like ports and in which,

his. l is a diaerumnuutic sectional elevation of on unnarutus tor themanufacture and treatment of cellulose derivetive sheets in accordancewith the invention, u portion oi the epparstus being hrolseu away tomore clearly show the internal structure.

it is u irsernentury sectionul elevation oi as portion oi the apparatusshown in Fig. i iilustrot" J the upnlicutlon oi on impregnating orcoutinu solution to the cellulose derivative sheeti i s. 3 end i arefragruentery elevationel views in nurtial section looting toward thewheel end in c, direction at right angles to that oi li ies. i end 2,illustrating the lower port of a casting wheel end the method icy whicha, striped product may he produced in accordance with specificenmtiodiments oi the invention.

Although relatlne portly to the coloring or r dyeing oi cellulose estersheeting, considered in its loroeder aspects, the invention includestroutins u cellulose clerivotive sheet with e solution or .ursnenslou toimport color or anti-static or other desired properties thereto, 'ttihcnusing on upptus such as that illustrated in Fig. i, l have discoveredthat this treatment of the cellulose derivative material may be bestaccomplished by cool the solution to the sheet at about the point whereit has been carried through one half, of a revolution on the castingwheel, although I do not limit myself to application of the solution atany particular point in the rotation of the wheel, specltying only'that'the solution isto he lit applied to the sheet before removal from thecasting surface.

I wish to emphasize that my process is especially characterized by thisfact, i. e., that the sheeting is impregnated with a dissolved orsuspended material before removal from the surface upon which it iscast-and that the dissolved or suspended components of the treatingliquid .is

deposited on or in the surface of the sheeting. and remains in thefinished product.

As pointed out above, the liquids usually employed for dyeing orotherwise treating cellulose derivative sheeting have a decided tendencyto cause wrinkling, buckling or distortion thereof. This is particularlytrue of liquids having a direct solvent action on the cellulosederivative material, although certain nonsolvent liquids producedistortion due to their swelling action on the material. I havediscovered that only when the treating liquid is applied to the sheetwhile still adhering to the casting surface can the desired propertiesbe imparted thereto without wrinkling or buckling. Even extremely thintypes of sheeting are amenable to treatment by my process without anyundesirable distortion whatever.

As will be readily understood, the original sheet-forming celluloseester solution or dope is spread upon the casting surface andimmediately begins to lose solvent by evaporation. The solvent will ofcourse evaporate from the outer surface of the dope much more rapidlythan it does from that portion next to the casting surface or, in otherwords, it tends to skin over, leaving that portion next to the castingsurface in a relatively more highly plastic condition than the outside.progressively as the casting surface rotates and the sheet tends to losemore and more of its solvent with the result that itshrinks to a certainextent and thereby clings very closely to the casting surface and liesperfectly flat thereon. 1 have found that if the treating solution isnow applied to the surface of the sheet it will penetrate at least theouter portions or layers thereof, but since the sheet is then shrunktightly onto the casting surface, it willcontinue to cling closelythereto and will not tend to wrinkle or buckle as would be the case ifthe treating liquid were applied after it had been removed therefrom. Asa matter of fact, I have found that, once the thin sheet has beenremoved from the casting surface, it cannot be successfully treated withimpregnating liquids without wrinkling or buck- It will'be apparent froma consideration of the facts just stated, that a sheet may be readilycolored by applying suitable dye solution thereto in the manner justspecified. Although per meation of the sheet by the solution will berelatively more complete when employing as the solvent for the coloringmatter an active solvent of the cellulose ester material, the processis, to all intents and purposes, equally successful when the solvent ismerely a swelling agent for the ester. This fact enables me to employboth solvents and non-solvents, although, I prefer to employ a celluloseester solvent rather than a non-solvent. It is of course possible to usea mixture of solvents and non-solvents and to control the solvent actionof any given mixture by increasing or decreasing the amount of dilutingnon-solvent in the mixture. Even a non-solvent treating solution may beused where the solution adheres sufficiently well to the sheeting.Typical suitable This initial curing action takes place non-solventliquids are toluene, benzene and heroin.

The particular solvent or non-solvent employed in making up my treatingsolution will of course depend largely upon the nature of the sheetingbeing treated, and to a certain extent, upon the added components of thetreating liquid. If it is desired, for example, to dye the ordinaryhydrolyzed cellulose acetate sheeting, a liquid comprising 50% acetoneand 50% methyl alcohol may be employed. Other appropriate solventliquids comprise a mixture of ethylene chloride and alcohol, ethylacetate, ethylene chloridetertiary amyl alcohol,.acetone-methylcellosolve (monomethyl ether of ethylene glycol), and many others. Whendealing with cellulose acetate-propionate, solvent liquids includeethylene chloride, ethyl acetate, methyl ethyl ketone and others. Itwill of course be understood that the nature of cellulose ester materialof the sheet must be taken into consideration when making up thetreating liquid and. the components of this liquid will be selected uponthe basis of their solvent or swelling action with respect to a givencellulose ester. The solubility of these esters in various agentsdiffer, not only with the particular solvent, but also with the degreeof hydrolysis of the ester and with amount of acyl group present in theester molecule. The effect of varying degrees of hydrolysis on thesolubility of mixed cellulose esters is more fully explained in theco-pending application of C. J. Malm and C. F.

Fletcher, Serial No. 551,546 filed July 17, 1931.

In the case of the fully esterified mixed esters the solubility in agiven solvent depends upon the ratio of the amounts of the differentacyl groups in a given ester as more fully set forth in the applicationof C. J. Malm and G. F. Nadeau, Serial No. 659,698, filed March 6, 1933.

While I find it convenient to illustrate my invention by reference tocellulose acetate sheet, it is in no sense limited to the treatment ofthis material, but broadly applicable to the dyeing or other treatmentof sheeting produced from a wide variety of single or mixed celluloseesters, such as cellulose nitrate, cellulose propionate, cellulosenitrate, cellulose acetate-propionate, cellulose acetate-butyrate,cellulose acetate-stearate and many others.

It is also to be understood that the cellulose ester solutions fromwhich the sheeting is cast may contain any suitable plasticizers. In thecase of cellulose acetate appropriate plasticizers include monoacetin,triacetin, monochlornaphthalene, camphor, tricresyl phosphate, triphenylphosphate, pentaerythritol tetracetate and many others known tothoseskilled in the art.

While I have just referred to the use ofsolutions or suspensions ofcoloring matter and to the coloring of cellulose ester sheeting, myinvention is in no sense limited to this specific treatment as it isequally applicable to the treatment of sheet material for many otherpurposes as will be more fully set forth. I may, for example, wish toapply thin coatings of various solid materials to the surface of thesheeting. I may, for example,'desire to apply certainlubricatingmaterials to the surface of thin cellulose ester materialdesigned for wrapping purposes to enable this type of sheeting to bemore rapidly passed through packaging machinery, or to treat the surfaceof a cinematographic film support with a lubricating agent to enable itto be more easily passed through a projection apparatus.

In the case of wrapping material it has been proposed in the U. S.patent to Alfred D. Slack and Albert A. Young, No. 2,011,348, issued onapplication Serial No. 673,038, flled May 26,1933.

to treat this type of sheeting with a solution of an agent which willprevent'the accumulation of static charges on its surface and will alsolubricate the material. In this case, the sheeting is treated with adilute solution of stearic acid in a cellulose ester non-solvent. I havefound that such a process may be most eflectively carried out inaccordance with the invention if the solution is applied to the sheetingbefore it has been stripped from the casting surface. I may in thismanner also employ various solutions of inorganic salts for improvingthe anti-static properties of the material such as Glaubers salt,lithium chloride, stannic chloride and. in fact, almost any metallicsalts which increase its electrical conductivity.

The practice of my invention will best be illustrated by reference to atypical example which is included merely for purposes of illustrationand in no sense as a limitation thereof.

Referring now to the drawing, the numeral i designates a. casting wheelmounted in suitable bearings f and provided with a suitable coatingsurface 3, preferably consisting of several different metallic layersplated one on top of the other. The numeral t designates a hoppercomprising a V-shaped container provided with a stationary blade and anadjustable blade t actuated by a suitable device, such as thumb screw l,for regulating the thickness of the stream of cellulose derivativesolution or dope ii flowing from the hopper onto the surface'ofthewheel.

The wheel i is completely surrounded by a casing 9 through which acurrent of heated air passes in the direction indicated by the arrows,the air being supplied to the casing by a blower or other appropriatemeans (not shown) through the hot air inlet i0, and, after passingaround the casing to the opposite side is evacuated therefrom by the airoutlet ll.

The numeral l2 designates a curing section directly connected to thecasing t and, in fact, forming an extension or continuation thereof. Thesection if is divided by a partition it into two compartments i l andIS. The compartment it is provided with a series of idle rolls l5 overwhich the sheet is passed after being stripped from the casting surface.The second compartment lltof the curing section is provided with dryingor curing drums ll over which the sheet is carried after leaving theidle rolls l5 of compartment i4. Guide rolls l8 serve to convey thecured sheet to the wind-up roll l9 positioned opposite the door 20through which the finished material may be removed when desired.

The hot air inlet pipe l0 supplies both compartments l4 and i6 of thecuring section l2 with heated air which is led from these compartmentsby the air outlets 2| and 22, respectively.

Numeral 23 designates a hopper or tank, preferably' positioned at thelowest point of the casting surface, and partially or wholly enclosedbythe air casing 9. The hopper 23 may be provided with a suitable coverto prevent excessive evaporation of its contents and is provided with a-cylin'drical applicator roll 25 rotatably mounted therein and adaptedto be partially submerged in a body of treating solution 26 and toconvey a thin film of this solution into close proximity with thesurface of the casting wheel as roll I rotates in the directionindicated by the arrow at the upper part of the figure, the roll 25being driven in the direction indicated by the arrow appearing thereon.The hopper 23 is supplied with treating fluid'through the inlet pipe 32controlled by valve 33, the fluid, if desired, circulat-.

ing through the hopper and being discharged therefrom through outletpipe 34. It will ofcourse be understood that both the casting wheel andthe applicator roll are driven by appropriate mechanism, not shown.

Referring now to Fig. 2 which illustrates the method of application ofthe treating solution to the support or film and in which the relativesizes of the various elements have been somewhat exaggerated for thesake of clearness, it

will be seen that the applicator roll 25 dipping in the solution 26carries up a portion thereof and applies it to the surface of the film28 in the form of a bead fl. It will thus be seen that the roll ispositioned just close enough to the surface of the wheel to provide formaintaining this relatively fine head of solution in constant contactwith the film surface.

Referring to Fig. 3, the numeral 29 designates a special type of rollfor applying parallel colored stripes to the cellulose derivative sheetmaterial, the roll 29 dipping in the body of fluid 26 in the same manneras illustrated in Fig. 2 and applying the colored solution or suspensionas a plurality of small beads. l

In Fig. 4 there is illustrated a. still different type of roll 30 forapplication of diagonal stripes to the sheeting. The operation of thisroll 3b is in all respects similar to the operation of the roll .29shown in Fig. 3, except that the fluid 726 is carried up along theoutside of the spiral ii and is machined so that it is substantiallyparallel with the surface of the wheel l and, as in the two previousinstances, is spaced at small distance therefrom. W'hen emplo this typeof roll it is necessary that the roll turn in the di rection indicatedby the arrow thereon, that is,

in a direction such that the treating solution roll moves at the pointof contact in the same direction and at the same peripheral speed as thesheet to which it is applied' As shown in the drawing, the hopper 23 ismounted so as to protrude into the air casing 9, but since the hopper isof less width than the width of the wheel casing i, the air passingthrough the casing may pass around the hopper and is not obstructedthereby. In some cases it may be desirable to form the walls of thecasing i so as to protrude outwardly to provide additional space oneither side of the hopper 23 for thepassage of the air through thecasing.

Although I have shown a single hopper adapted for the application of onetreating or impregnating solution at a time, I may employ a. pluralityof hoppers to provide for the successive application of a number ofdifferent solutions or suspenslons to the sheet. For example, it may bederolls and containing the desired color, mounted one ahead of theotherat the bottom of the wheel casing and appropriately spaced. In such anarrangement the first hopper will supply one color which will be carriedup onto the surface of the sheet by means of an appropriate roll simtionis as follows.

ilar to roll 25, while each succeeding hopper and its r011 will supplyadditional colors 'as desired. It will, of course, be necessary to spacethe respective hoppers at such a distance from one another as willpermit a sufficient amount of evaporation or' drying out of solventcontained in the coloring liquids to take place to prevent running orsmudging. Such details of construction and operation are obviouslywithin the province port or even emulsioned film for the purpose of edgemarking and involving the use of -various forms of edge marking rolls.An example of the latter. process is contained in the co-pendingapplication of K. C. D. Hickman, Serial No. 362,844, filed May 13, 1929.

Although the carrying out of my process will be fairly evident from aconsideration of the several figures of the drawing, briefly stated, theopera- A cellulose ester dope, for example, a solution consisting of onepart by weight of the acetone-soluble variety of cellulose acetatedissolved in four to six parts by weight of acetone is placed in thehopper 4 from which it is fed in suitable thickness and at anappropriate temperature to the surface of the coating wheel I. As thewheel rotates in the direction indicated by the arrow, a thin layer ofsolution is continual-v ly spread upon the wheel and solvents arerapidly evaporated therefrom by the current of heated air passing aroundthe wheel surface through the casing 9. This evaporation takes placeprogressively until the'sheet contains, say, only .a few percent ofsolvents in which condition it may then be readily stripped from thewheel and passed through the curing section. When the sheet reaches thelowermost position in the casing it meets solution 26 carried up by therotating roll 25 and is readily permeated thereby. When the solution 26contains dyes or other coloring matter, for example, these are carriedwell into the body of the film and, in fact, may in some casescompletely penetrate the full thickness of the film. Not only is thesheet penetrated by the solution, but, due to the fact that it clingsclosely to the casting surface when the treating solution is appliedthereto, it has no tendency to wrinkle or buckle away from the coatingsurface and, in fact, has exactly the opposite tendency, that is, apositive tendency to shrink closer thereto and lie perfectly flatthereon. It is this fact that makes possible the successful treatment ofeven extremely thin sheeting by my process.

The treated sheet, after stripping from the casting surface, issubjected to any desired curing operation, such as by carrying itthrough the various compartments of the curing section I 2 where it issubjected to an additional current of warm air to remove any residualsolvents and to give the film its proper shrinkage characteristics.

As pointed out above, the invention is of rather broad scope andincludes various types of film treatment. As indicated, one ofthe mostimportant applications is in the coloring of thin sheeting. A suitablesolution for color treatment may comprise the following:

Butyl acetate 100 The above solutiorris of course only typical ofmany'which may be employed for cellulose acetate or other types ofcellulose ester thin sheeting. In addition to acetone-soluble dyes otherdyes such as the following may be successfully employed.

Color Index No.

In addition other coloring material, such as suspensions of variousfinely divided vegetable and mineral coloring matters, metallic powderssuch as gold, silver and bronze powders, pigments such as titaniumdioxide, lithopone, baryta, and other materials may be employed.

If it is desired to impregnate or coat the cellulbse derivative sheetingwith solid material such as stearic acid, in accordance with theprocedure outlined in the above mentioned Slack and Young application,the following formula may be employed:

Grams Stearic acid -4 40 Acetone 700 Butyl acetate 260 As aboveindicated, in some cases it may be desirable to impregnate the sheetingin this manner with a solution of a metallic salt such as lithium orstannic chloride to give it anti-static properties. The salt may beapplied in the form of a separate solution or may be added to a coloringsolution. For example, when employing a separate solution for thispurpose, it may con tain 2% lithium chloride and 5% glycerine dissolvedin a mixture of 10% water and acetone.

If it is desired to render the sheeting hygroscopic, glycerine may beincorporated with a given treating solution, this being carried into theinterior of the sheet and being retained thereby after curing iscompleted.

The invention also includes applying coatings or layers of variousmaterials to the sheeting. It may, for example, be desired to apply athin coating of gelatin in which case the treating solution may comprisea few percent of gelatin dissolved in a mixture of acetone and water inwhich the acetone preferably predominates. Coatings of cellulose estersmay also be applied in accordance with the invention. For example, I maycoat a sheet of cellulose acetate with cellulose nitrate by applying adilute solution of the nitrate in methyl alcohol or in a mixture ofmethyl alcohol and acetone. In any of these cases, in accordance withthe invention, the sheeting is treated before removal from, andtherefore clinging closely to, the casting surface and the liquid issuch that it slightly attacks the plastic material or at leastpenetrates thereinto.

The invention is to be distinguished from known processes involving theapplication of solutions as suspensions to the surface of sheeting tobuild up a thin layer thereon as in such processes, not only is adefinite and distinct layer or stratum built up by such treatment, butthere is no appreciable penetration or permeation of Fuchsin Y 677Spirit red 258' Acid green L 666 Malachite green 657 Oil orangeE 24;Methanil yellow; -138 Fast wool yellow 3 g 636 ,Fast wool blue B 209Spirit blue 689 Spirit nigrosine 864 lit lit

aoeasvv the sheet by the liquid. Furthermore, in these cases the sheetis not treated until the sheet is stripped from the wheel whereasaccording to the present invention the treatment can be carried out onlybefore the sheet is stripped from the casting surface.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent of the United States is:

l. The process which comprises casting a cellulose ester solution in theform of a sheet on an appropriate surface, allowing the sheet to set byevaporation of solvent therefrom, and treating the sheet before removalfrom the casting surface and while the sheet contains an appreciableamount oi residual solvent with a dye solution.

2. The process which comprises casting a cellulose ester solution in theform of a sheet on an appropriate surface, allowing the sheet to set byevaporation of solvent therefrom, and treating the sheet, before removalfrom the casting surface and while the sheet contains an appreciableamount of residual solvent with a dye dissolved in a liquid containingan active solvent of the cellulose ester.

3. The process which comprises casting a cellulose ester solution in theform of a sheet on an appropriate surface, allowing the sheet to set byevaporation of solvent therefrom, and treating the sheet, before removalfrom the casting surface and while the sheet contains an appreciableamount of residual solvent with a dye dissolved in a liquid containingan active solvent of the cellulose ester and a non-solvent.

t. The process which comprises casting a ce1lulose ester solution in theform of a sheet on an appropriate surface, allowing the sheet to set byevaporation of solvent therefrom, and treating the sheet before removalfrom the casting surface and while the sheet contains all appre ciableamount of residual solvent with a solution at a lubricating agent.

5. The process which comprises casting a cellulose estersolution in theform ot a sheet on an appropriate allowing the sheet to set byevaporation of solvent therefrom and treating the sheet before removalfrom the casting surface and while the sheet contains an appreciableamount of residual solvent with a solution oi stearic acid.

6. The process which comprises casting a cellulose acetate solutioninthe form of a sheet on an appropriate surface, allowing the sheet toset by evaporation of solvent therefrom, and treating the sheet, beforeremoval from the casting surface and while the sheet contains an appre-'ciable amount of residual solvent with an acetone solution of dye.

7. The process of applying color in the term of stripes to cellulosederivative sheeting which comprises applying a dye solution thereto inthe form of a plurality of beads before the sheeting is removed from thesurface on which it is cast and while the sheeting still contains anappreciable amount of residual solvent.

8, The process 01 coloring cellulose acetate sheeting which comprisesapplying to the sheeting before removal from the surface on which it iscast and while still containing an appreciable amount of residualsolvent, a colored solution which contains a liquid which substantiallypene trates the body of the sheeting and permanently deposits the colorwithin the structure thereof.

9. The process of making a cellulose ester sheeting having a permanentgelatin coating thereon which comprises casting a cellulose estersolution in the form of a sheet on an appropriate surface, allowing thesheetto set by evaporation of solvent therefrom, and applying to thesheet before removal from the casting surface and while the sheetcontains an appreciable amount of residual solvent, a gelatin solutioncontaining a liquid which penetrates into the body of the sheet.

10. The process of making a cellulose organic ester sheeting having apermanent gelatin coating thereon which comprises casting a celluloseorganic ester solution in the form of a sheet on an appropriate surface,allowing the sheet to set by evaporation of solvent therefrom, and

applying to the sheet before removal from the casting surface and whilethe sheet contains an appreciable amount of residual solvent, a gelatinsolution containing a liquid which penetrates into the body of thesheet.

11. The process of making a cellulose nitrate sheeting having apermanent gelatin coating thereon which comprises casting a. cellulosenitrate solution in the form of a sheet on an appropriatesurface,allowing the sheet to set by evaporation of solvent therefrom, andapplying to the sheet before removal from the casting surface and whilethe sheet contains an appreciable amount of residual solvent, a gelatinsolution containing a liquid which penetrates into the body of thesheet.

l2. The process of making a cellulose acetate sheeting having apermanent gelatin coating thereon which comprises casting a celluloseacetate solution in the form of a sheet on an appropriate surface,allowing the sheet to set by evaporation of solvent therefrom, andapplying to the sheet before removal from the casting surface and whilethe sheet contains an appreciable amount of residual solvent, at gelatinsolution containing a liquid which penetrates into the body of thesheet.

JACKSON B. WELLS.

